Nicotine regulates 5-HT1A receptor gene expression in the cerebral cortex and dorsal hippocampus

The 5-HT1A receptor has previously been shown to be important in mediating the behavioural effects of nicotine. It is possible that nicotine administr ation might regulate the levels of 5-HT receptors in limbic and cortical re gions, and such regulations may underlie adaptive responses to nicotine in the central nervous system. The effects of acute and chronic systemic (-)-n icotine administration on 5-HT1A receptor gene expression were measured by in situ hybridization, in the rat cerebral cortex, dorsal hippocampus and l ateral septum. In the cortex, acute nicotine (0.5 mg/kg i.p.) significantly increased the expression of 5-HT1A receptor mRNA 2 h and 24 h after inject ion. Similarly, acute nicotine significantly increased 5-HT1A receptor mRNA in the dentate gyrus (DG), CA3 and CA1 regions of the dorsal hippocampus 2 h and 24 h after injection. Acute nicotine was without effect in the later al septum. Chronic nicotine (0.5 mg/kg i.p; twice daily for 7 days) signifi cantly decreased 5-HT1A receptor mRNA in the cortex 2 h after the final inj ection, but was without effect at 24 h or 72 h. Chronic nicotine caused no changes in 5-HT1A mRNA in the lateral septum or dorsal hippocampus. These d ata demonstrate that nicotine regulates 5-HT1A receptor gene expression in the cortex and hippocampus. The rapid regulation of expression of 5-HT1A re ceptor mRNA leads to the hypothesis that nicotine-induced 5-HT release may alter the postsynaptic sensitivity to 5-HT.